We’ve all been there. We try pouring ketchup onto our fries from the bottle, but it doesn’t come out. So we tap the back of the bottle a few times, and suddenly, the ketchup rushes out and your entire meal is covered with it. Why does the ketchup exhibit such behavior?
The shape of a container can affect the flow of the fluid inside it. Water in a narrow stream flows smoothly, but once the water molecules make their way into a pond, they spread out and no longer flow coherently. If you blow into a long, narrow straw, the air will go straight through. Once the air flows into the large room you are standing in, it slows down as it mixes with the air around it, so someone standing five feet away from you won’t feel a breeze at all. The above examples show how the shape of a container affect the flow of passive fluids. In today’s study, Kun-Ta Wu and colleagues investigated how the motion of active fluids, fluids that flow using an internal source of energy, is also affected by the shape of their container. They used a system of microtubules, chains of proteins assembled into long, stiff rods. Clusters of a protein called kinesin exert a force on microtubules by “walking” along them. Microtubules interact with each other to form swarms or turbulent-like flows.
Cells have to do an awful lot of tasks correctly and on time in a noisy and unpredictable environment. How do they do it? In this post, we look at one particular process, making proteins, and learn how cells operate away from thermodynamic equilibrium in order to make the right protein at the right time over and over again.
If you were Spider-Man, how would you catch your criminals? You could tangle them up in different types of threads, but to really keep them from escaping you probably want your web to be sticky (not to mention the utility of sticky silk for swinging between buildings) ...
“One day it's fine and next it's…” red? Microscopic algae depend on photosynthesis, so they follow light. Previous research has shown that their swimming is directed towards white light but not to red light. New work shows that light-activated stickiness allows microscopic algae to switch between different movement methods.
Many living creatures, such as birds, sheep, and fish, make coherent flocks or swarms. Flocking animals travel together, coordinating their speed and turns in an often visually striking manner. This can have benefits for the animals – flocking birds can use aerodynamics to fly more efficiently, sheep can move together as a group to evade predators, and fish can use collective sensing to find preferred locations in their environment. Flocks emerge in biological systems because animals try to follow their neighbors. But how about non-living things? Can they spontaneously form swarms without any biological motive?
Place yourself in a bumper car at a carnival waiting to bump into your friends. Soon enough you hear the small engine of your bumper car start and you begin to move around, bumping into anyone in your way. While the motion of your car is mostly controlled by the steering wheel, random events---like fluctuations in the motor power, your car hitting small bumps on the floor, and other cars hitting you---can affect the motion as well. What if I told you that a cell and its parts function in a similar way? Just as your car is powered by electricity, molecular motors---bio-molecules that can convert chemical energy into mechanical work---power the movement of living organisms by generating forces. In order to produce these forces, molecular motors depend on an organic molecule called ATP.
Have you ever seen those wide shapes moving in the sky at dawn, made of thousands of starlings, or the swarms of fish swimming in the ocean (see Figure 1)? The ability to organize and move in groups without a leader is called collective motion and has been observed at various spatial scales in the living world, from birds to locusts, cells, and bacteria.
The difference between a bacterium and a whale are huge, and not just their size. However, there are hidden scaling laws underlying all living things. These scaling laws are found to be due to the fractal-like nutrient distribution systems. Here, we review how to derive the scaling law for metabolic rate with organism mass, illustrating its generality and ubiquity.
One of the greatest challenges of making proton exchange membrane fuel cells is designing the membrane after which they are named. Engineers would love to have a membrane that transports protons quickly and efficiently. Although there are polymeric materials (e.g. Nafion) that can do this fairly well, there is still a need for faster transport. This week’s paper investigates the role of a polymer’s “precise” structure in facilitating fast proton transport.